1. Field of the Invention
This invention relates to an actuating device for a shutter of the type which employs a piezoelectric element as an actuating element.
2. Description of the Prior Art
A shutter actuating device is required to be accurate in exposing operation. In particular, a shutter actuating device is required that it be accurate in aperture and also accurate in time until a predetermined aperture position is reached. Where a shutter is actuated using, as an actuating element, a piezoelectric element such as a bimorph element which produces an actuating force when a voltage is applied thereacross, a required aperture accuracy can be readily realized if a photocoupler or a like element is used. However, the accuracy in time until a predetermined aperture position is reached depends upon the stability of the charging speed of the bimorph element when a voltage is applied across the bimorph element because the actuating force produced by the bimorph element increases in proportion to the voltage applied which in turn increases in proportion to the charge accumulated in the bimorph element and accordingly the bimorph element can be regarded as a capacitor. Conventional methods involve supply of shaped pulse current to charge up a bimorph element as disclosed in Japanese Patent Laid-Open No. 60-149033. However, such methods necessitate a pulse generator. Consequently, there is a problem that the system is complicated in construction and accordingly is high in cost.